The invention relates to a control system for an internal combustion engines of agricultural or commercial vehicles, in particular for engines of agricultural tractors.
Agricultural tractors are designed with respect to desired values of drawbar force and desired gearbox speeds. A standard tractor for plowing at 6 to 7 kilometers per hour (km/h), for example, is designed for a power output of 100 DIN-kW. In order to apply the necessary drawbar force to the ground, the tractor is equipped with heavy weights and large tires. The lower the operating speed is, the greater the torques that can be transmitted at constant engine power output. At low speeds, for example, below 6 km/h, the components of the driveline are protected against overloads by the slip of the wheels. A standard tractor with an output of 100 DIN-kW can pull a trailer of 20 t on a track that rises 1.5 m in a distance of 100 m (upgrade of 1.5%), at a maximum speed of 50 km/h.
Tractors are increasingly driven longer distances on roads, during which higher speeds are desired. For example, it is desirable for a tractor to pull a trailer of 20 t on an upgrade of 1.5% at a speed of 65 km/h. However, this requires an engine power output of approximately 130 kW. For a speed of 80 km/h approximately 168 kW are required. In order to attain these speeds, the engine, the tractor support structure and all other tractor components must be designed for the stated power output values. For operation in the field, however, the drive system of such a tractor would be over-designed and hence uneconomical. As a point of reference, it can be assumed that an overload of the vehicle components by 10% will reduce their service life by approximately 30%.
With an optimum design differing tractors result for operation on the field and the transport over roads, whose internal combustion engines, drivelines, support structures and other tractor components must be designed for differing power output or load capacity. This is in opposition to the desire to offer tractors at favorable cost for a wide range of applications. Since on the one hand, an efficient and hence low cost manufacturing is possible only with the lowest possible number of models and, on the other hand, the use of over-designed drivelines lead to increased costs.